For making steel, solid pieces of ferrous metal such as scrap, pellets, etc., are melted down to form a melt which can be worked to the composition and characteristics desired for casting.
When the working is done by the ASEA-SKF practice, the melt is poured into a ladle furnace, of which there may be more than one, the ladle furnace being crane-carried and inserted in an AC induction coil for stirring, the ladle shell being non-magnetic. A roof is provided which can be lowered on the ladle and through which arcing electrodes project for adding heat to the melt, and also there is a cover which can be lowered on the ladle's top and evacuated for degassing the melt. In this way additions can be stirred into the melt, the melt can be further heated, and if desired, finally degassed. The ladle can be used for casting in the same way any steel ladle is used. This practice is disclosed by British specification No. 1,112,876.
To supply the melt required, it is most customary to charge steel scrap, pellets and possibly other solid ferrous pieces into an electric arc furnace having powered arcing electrodes, the arcs boring down into the pieces until ultimately a complete melt-down is effected. During this melt-down, there is arcing from piece to piece of the solid metal which produces concussions and smoke while introducing disturbances in the electrical network supplying the arcing electrode power. The furnace hearth and wall linings are subject to extremely high temperatures and erosion and must be repaired or replaced frequently. The arcing electrodes are consumable, and their cost of replacement is high. It is desirable to provide some better way for effecting a melt-down.
One other way is by the use of a crucible electric AC induction furnace, but this is time-consuming because it cannot be used with the same high power concentrations as can an arc furnace. When used for a melt-down, a crucible induction furnace is particularly sensitive to crucible leakage which damages its induction coil or coils and causes an expensive shutdown.
The object of the invention described below is to provide a better way for effecting a melt-down of solid pieces of metal so as to form a melt.